Re: [PATCH 6/7] hw/{arm,hppa,riscv}: Add fw_cfg arch-specific stub

[Laszlo Ersek <lersek@redhat.com>]

On 04/26/21 21:35, Philippe Mathieu-Daudé wrote:
> The ARM, HPPA and RISC-V architectures don't declare any fw_cfg
> specific key. To simplify the buildsys machinery and allow building
> QEMU without the fw_cfg device (in the next commit), first add a
> per-architecture empty stub defining the fw_cfg_arch_key_name().
> 
> Update the MAINTAINERS section to cover the various target-specific
> fw_cfg.c files.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/arm/fw_cfg.c      | 19 +++++++++++++++++++
>  hw/hppa/fw_cfg.c     | 19 +++++++++++++++++++
>  hw/riscv/fw_cfg.c    | 19 +++++++++++++++++++
>  MAINTAINERS          |  2 +-
>  hw/arm/meson.build   |  1 +
>  hw/hppa/meson.build  |  1 +
>  hw/riscv/meson.build |  1 +
>  7 files changed, 61 insertions(+), 1 deletion(-)
>  create mode 100644 hw/arm/fw_cfg.c
>  create mode 100644 hw/hppa/fw_cfg.c
>  create mode 100644 hw/riscv/fw_cfg.c

So, I haven't commented on the Kconfig symbol wrangling yet (my comment
would be a blanket "Acked-by" anyway... sorry, not really my cup of
tea), but at this point:

I don't understand why we need to add *more code* (stubs / boilerplate)
if our goal is (apparently) to build QEMU with *fewer* devices.

Sorry for being dense. My total knowledge about stubs in QEMU is this:
for some QMP methods (and for some QGA methods, dependent on OS), we
need stubs. When they are invoked, they report "sorry, not implemented".
That's it: all I know about stubs.

So... the commit message here says "simplify the buildsys", and the next
commit message says, paraphrased, "don't build fw_cfg unless we need it"
-- but why does that require more C-language code? It seems like we have
some function *calls* that shouldn't exist in an fw-cfg-less machine, in
the first place.

Again, sorry, I'm totally dense on this.

Thanks
Laszlo

> 
> diff --git a/hw/arm/fw_cfg.c b/hw/arm/fw_cfg.c
> new file mode 100644
> index 00000000000..de2bca9c76c
> --- /dev/null
> +++ b/hw/arm/fw_cfg.c
> @@ -0,0 +1,19 @@
> +/*
> + * QEMU fw_cfg helpers (ARM specific)
> + *
> + * Copyright (c) 2021 Red Hat, Inc.
> + *
> + * Author:
> + *   Philippe Mathieu-Daudé <philmd@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/mips/fw_cfg.h"
> +#include "hw/nvram/fw_cfg.h"
> +
> +const char *fw_cfg_arch_key_name(uint16_t key)
> +{
> +    return NULL;
> +}
> diff --git a/hw/hppa/fw_cfg.c b/hw/hppa/fw_cfg.c
> new file mode 100644
> index 00000000000..322b03068c7
> --- /dev/null
> +++ b/hw/hppa/fw_cfg.c
> @@ -0,0 +1,19 @@
> +/*
> + * QEMU fw_cfg helpers (HPPA specific)
> + *
> + * Copyright (c) 2021 Red Hat, Inc.
> + *
> + * Author:
> + *   Philippe Mathieu-Daudé <philmd@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/mips/fw_cfg.h"
> +#include "hw/nvram/fw_cfg.h"
> +
> +const char *fw_cfg_arch_key_name(uint16_t key)
> +{
> +    return NULL;
> +}
> diff --git a/hw/riscv/fw_cfg.c b/hw/riscv/fw_cfg.c
> new file mode 100644
> index 00000000000..8e3d2a8bdea
> --- /dev/null
> +++ b/hw/riscv/fw_cfg.c
> @@ -0,0 +1,19 @@
> +/*
> + * QEMU fw_cfg helpers (RISC-V specific)
> + *
> + * Copyright (c) 2021 Red Hat, Inc.
> + *
> + * Author:
> + *   Philippe Mathieu-Daudé <philmd@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/mips/fw_cfg.h"
> +#include "hw/nvram/fw_cfg.h"
> +
> +const char *fw_cfg_arch_key_name(uint16_t key)
> +{
> +    return NULL;
> +}
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 36055f14c59..ab8f030d4c0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2162,7 +2162,7 @@ R: Laszlo Ersek <lersek@redhat.com>
>  R: Gerd Hoffmann <kraxel@redhat.com>
>  S: Supported
>  F: docs/specs/fw_cfg.txt
> -F: hw/nvram/fw_cfg*.c
> +F: hw/*/fw_cfg*.c
>  F: stubs/fw_cfg.c
>  F: include/hw/nvram/fw_cfg.h
>  F: include/standard-headers/linux/qemu_fw_cfg.h
> diff --git a/hw/arm/meson.build b/hw/arm/meson.build
> index be39117b9b6..fd278de916f 100644
> --- a/hw/arm/meson.build
> +++ b/hw/arm/meson.build
> @@ -1,6 +1,7 @@
>  arm_ss = ss.source_set()
>  arm_ss.add(files('boot.c'), fdt)
>  arm_ss.add(when: 'CONFIG_PLATFORM_BUS', if_true: files('sysbus-fdt.c'))
> +arm_ss.add(when: 'CONFIG_FW_CFG', if_true: files('fw_cfg.c'))
>  arm_ss.add(when: 'CONFIG_ARM_VIRT', if_true: files('virt.c'))
>  arm_ss.add(when: 'CONFIG_ACPI', if_true: files('virt-acpi-build.c'))
>  arm_ss.add(when: 'CONFIG_DIGIC', if_true: files('digic_boards.c'))
> diff --git a/hw/hppa/meson.build b/hw/hppa/meson.build
> index 1deae83aee8..10494cc24b7 100644
> --- a/hw/hppa/meson.build
> +++ b/hw/hppa/meson.build
> @@ -1,4 +1,5 @@
>  hppa_ss = ss.source_set()
>  hppa_ss.add(when: 'CONFIG_DINO', if_true: files('pci.c', 'machine.c', 'dino.c', 'lasi.c'))
> +hppa_ss.add(when: 'CONFIG_FW_CFG', if_true: files('fw_cfg.c'))
>  
>  hw_arch += {'hppa': hppa_ss}
> diff --git a/hw/riscv/meson.build b/hw/riscv/meson.build
> index 275c0f7eb7c..ab4d3adb924 100644
> --- a/hw/riscv/meson.build
> +++ b/hw/riscv/meson.build
> @@ -8,5 +8,6 @@
>  riscv_ss.add(when: 'CONFIG_SIFIVE_U', if_true: files('sifive_u.c'))
>  riscv_ss.add(when: 'CONFIG_SPIKE', if_true: files('spike.c'))
>  riscv_ss.add(when: 'CONFIG_MICROCHIP_PFSOC', if_true: files('microchip_pfsoc.c'))
> +riscv_ss.add(when: 'CONFIG_FW_CFG', if_true: files('fw_cfg.c'))
>  
>  hw_arch += {'riscv': riscv_ss}
>